This invention relates to a pneumatic actuator and, more particularly, to a water proof structure for a pneumatic actuator for driving an external load drive wire which is used for controlling the degree of opening of an engine throttle valve.
FIG. 1 is a sectional view of a conventional pneumatic actuator to which the present invention pertains, and FIG. 2 is a partial sectional view taken along line II--II of FIG. 1.
In FIGS. 1 and 2, reference numeral 1 is a housing, 1s (FIG. 2) is a water proof side wall, 2 is an outer case, 3 is a connector fitting to which an external load drive wire (not illustrated) connected to an engine throttle valve (not illustrated) can be connected, 4 is a holding plate to which the connector fitting 3 is attached, 7 is a diaphragm which is securely attached at its outer periphery to the housing 1 or the outer case 2 and which is held at its central portion by the holding plates 4, 5 is a spring urging the holding plate 4 and the diaphragm 7 in the right hand direction in the figure, 6 is a diaphragm chamber defined by the housing 1 and the diaphragm 7, 8 is an air exhaust solenoid valve for opening and closing an exhaust conduit communicating the diaphragm chamber 6 to a vacuum source such as an engine air intake manifold (not shown), 9a and 9b are a pair of air intake solenoid valves for opening and closing air intake conduits communicating the diaphragm chamber 6 to a negative pressure source (not shown), 10 is an outer cover for protecting the exhaust solenoid valve 8 and the intake solenoid valves 9a and 9b, 11 is a plate for the solenoid valves, 12 is a clearance defined between an edge of the outer cover 10 and an outer circumferential surface of a valve mounting portion of the housing 1 and reference numeral 20 is a conduit communicating with the atmosphere.
When the pneumatic actuator as above described is used for controlling the degree of opening of the automobile throttle valve, the connector fitting 3 is connected to one end of an external load drive wire (not shown) connected to the throttle valve (not shown). In an accelerating mode, an external control unit (not shown) causes the exhaust solenoid valve 8 to open the negative pressure conduit. Then the negative pressure source such as an engine intake manifold (not shown) reduces the pressure within the diaphragm chamber 6, whereby the holding plate 4 and the connector fitting 3 are moved to the left in FIG. 1 against the action of the compression spring 5 to pull the external load drive wire (not shown) to open the engine throttle valve (not shown).
On the other hand, in a deceleration mode, the external control unit (not shown) causes the exhaust solenoid valve 8 to close the negative pressure conduit and causes the intake solenoid valves 9a and 9b to open the conduit communicated to the atmosphere. Then the pressure within the diaphragm chamber 6 becomes an atmospheric pressure, whereby the holding plate 4 and the connector fitting 3 are moved to the right in FIG. 1 by the action of the compression spring 5 to allow the external load drive wire (not shown) to return to close the engine throttle valve (not shown).
In the conventional pneumatic actuator, the outer cover 10 is mounted to the housing 1 so that its edge defining the opening extends horizontally and is spaced apart from the outer circumferential surface of the valve mounting portion of the housing 1 to define the substantially horizontally extending clearance 12 therebetween. In order to prevent water from entering into the interior of the outer cover 10, a solenoid valve mounting plate 11 having a width substantially closing the interior of the outer cover 10 is disposed between the valve mounting surface of the housing 1 and the solenoid valves 8, 9a and 9b.
However, in the conventional pneumatic actuator, water drops on the actuator from above is led to flow through the clearance 12 defined between the housing 1 and the outer cover 10 surrounding the solenoid valves 8, 9a and 9b, so that the water resistance is not very high.